Investigation Of The Spatial Coherent Effects In Some X-ray Imaging Techniques

X-ray imaging methodology is an important aspect of the X-ray imaging technology research. X-ray imaging methodology has been made great progress in recent years, especially for the applications of clinical medicine, life science, material science, information science, and a variety of industrial fields. Beginning from the history of X-ray imaging technology, we summarize the state of the art of the X-ray microscopy and X-ray phase contrast imaging. Due to the coherence effects on the quality of the imaging results, our thesis mainly base on the partial coherence theory. Through theoretical analysis and numerical simulation, we evaluate several important experiment platforms. At the same time, we propose the new design of transmission X-ray microscopy layouts. Our thesis mainly achieves the following results:1. Based on the diffraction theory and the partial coherence theory, the image-forming progresses of the2d grating interferometer and fractal zone plate based transmission X-ray microscope are derived in detail. Our thesis presents a general analysis for the study of X-ray partial coherence, and paves the way for subsequent performance analysis of X-ray imaging platforms.2. The recent use of one-dimensional X-ray Talbot interferometer has triggered a great interest to X-ray differential phase contrast imaging. As an improved version of a one-dimensional interferometer, the development of the two-dimensional grating interferometry strongly stimulated applications of grating-based imaging. In the framework of the Fresnel diffraction theory, we investigated the self-image of two-dimensional phase gratings under a partially coherent illumination. The fringe visibility of the self-image has been analyzed as a function of the spatial coherence length. From the view point of the self-image visibility, it is possible to find the optimal two-dimensional grid for two-dimensional X-ray grating interferometry imaging. Numerical simulations have been also carried out for a quantitative evaluation. Results, in good agreement with the theoretical analysis, indicate the spatial coherence requirements of the radiation illuminating a two-dimensional grating interferometry. Moreover, our results can be used to optimize performances of a two-dimensional grating interferometry and for further theoretical and experimental researches on grating based imaging systems. 3. In this contribution we discuss the possibility to design a modified Transmission X-ray microscope using fractal zone plates (Fzps) as diffractive optical elements. In the modified Transmission X-ray microscope optical layout, we first introduced a fractal zone plate as the microscope condenser. Using a fractal zone plate as a condenser we also simulated an axial irradiance. Results confirm that fractal zone plates can improve focusing capability with an extended depth of field. Although preliminary, these simulations clearly point out that fractal zone plates when available will be of great help in microscope layouts, in particular for foreseen high-resolution applications in the "water window" as strongly required in biological researches.4. One of the main benefits of a fractal plate is the formation of a sequence of subsidiary foci when used as a condenser. In order to further demonstrate the reliable use of a fractal zone plate in a transmission X-ray microscope, we studied how a condenser fractal zone plate affects the focal spot in a transmission X-ray microscope layout. We present and discuss the comparison in the X-ray region with a normal condenser zone plate and a numerical simulation that points out that the efficiency of the condenser depends by the structure and the material of the zone plate, and by the energy.5. Indeed, a fractal zone plate can be utilized as a condenser element to achieve an extended depth of field but also as an image-forming component. The design parameters are based on the real TXM instrument installed at the Beijing Synchrotron Radiation Facility (BSRF). Numerical analysis point out that fractal zone plates and conventional Fresnel zone plates have similar imaging capabilities under different coherent illuminations. This analysis paves a way for foreseen optical applications of modified zone plates in real microscope layouts.